Improved modeling of dynamic quantum systems

Many important applications in biochemistry, materials science, and catalysis sit squarely at the interface between quantum and statistical mechanics: coherent evolution is interrupted by discrete events, such as binding of a substrate, isomerization, or chemical exchange. Often these effects are detected by the changes they make to a molecular spectrum (rotational, vibrational, electronic, or nuclear spin) and the theoretical treatment of the effects of exchange on spectra were originally explored in detail in the late 1950's1,2. We recently discovered that the theory for incorporating chemical exchange into quantum evolution was incorrect, having made false statistical assumptions about the dynamics. We completely rebuilt this theoretical framework3,4, which led to the discovery of new physical effects as well as significant computational improvements for no additional cost; more recently, we have extended this to correct the Lindblad formulation of exchange usually used in problems such as ion trap dynamics4. I will focus on one important application, understanding a relatively new technique for producing very large nuclear magnetization called SABRE (Signal Amplification By Reversible Exchange), which can generate on the order of 10,000-fold enhancement of magnetic resonance signals in under a minute. SABRE uses para-hydrogen, perhaps the only "quantum reagent" stable at room temperature, to create large magnetization in other molecules in solution. It uses bizarre field conditions very different from "normal" magnetic resonance at many Tesla (typically, <1 mT, which is about 1% of the Earth's field) and thus the theoretical aspects were underexplored. Combining theoretical and experimental efforts for this problem has permitted significant improvements in the both the scope5,6 and performance7,8 of this method. 1 Kaplan, J., J. Chem. Phys., 29, 462 (1958); 2 Alexander, S., J. Chem. Phys., 37, 967 (1962); 3 Lindale, J., Sci. Adv., 6, eabb6874 (2020); 4 Lindale, J., Under Review (2022); 5 Lindale, J., J. Magn. Reson., 307, 106577 (2019); 6 Lindale, J., Phys. Chem. Chem. Phys., 24, 7214 (2022); 7 Eriksson, S., Sci. Adv., 8, eabl3708 (2022) 8 Li, X., Phys. Chem. Chem. Phys., 24, 16462 (2022)